switch to use gliderlabs/ssh for builtin server (#7250)

resolves git conflicts from #3896 (credit to @belak, in case github doesn't keep original author during squash)

Co-Authored-By: Matti Ranta <techknowlogick@gitea.io>

vendor/github.com/gliderlabs/ssh/context.go

@@ -0,0 +1,152 @@
+package ssh
+
+import (
+	"context"
+	"encoding/hex"
+	"net"
+	"sync"
+
+	gossh "golang.org/x/crypto/ssh"
+)
+
+// contextKey is a value for use with context.WithValue. It's used as
+// a pointer so it fits in an interface{} without allocation.
+type contextKey struct {
+	name string
+}
+
+var (
+	// ContextKeyUser is a context key for use with Contexts in this package.
+	// The associated value will be of type string.
+	ContextKeyUser = &contextKey{"user"}
+
+	// ContextKeySessionID is a context key for use with Contexts in this package.
+	// The associated value will be of type string.
+	ContextKeySessionID = &contextKey{"session-id"}
+
+	// ContextKeyPermissions is a context key for use with Contexts in this package.
+	// The associated value will be of type *Permissions.
+	ContextKeyPermissions = &contextKey{"permissions"}
+
+	// ContextKeyClientVersion is a context key for use with Contexts in this package.
+	// The associated value will be of type string.
+	ContextKeyClientVersion = &contextKey{"client-version"}
+
+	// ContextKeyServerVersion is a context key for use with Contexts in this package.
+	// The associated value will be of type string.
+	ContextKeyServerVersion = &contextKey{"server-version"}
+
+	// ContextKeyLocalAddr is a context key for use with Contexts in this package.
+	// The associated value will be of type net.Addr.
+	ContextKeyLocalAddr = &contextKey{"local-addr"}
+
+	// ContextKeyRemoteAddr is a context key for use with Contexts in this package.
+	// The associated value will be of type net.Addr.
+	ContextKeyRemoteAddr = &contextKey{"remote-addr"}
+
+	// ContextKeyServer is a context key for use with Contexts in this package.
+	// The associated value will be of type *Server.
+	ContextKeyServer = &contextKey{"ssh-server"}
+
+	// ContextKeyConn is a context key for use with Contexts in this package.
+	// The associated value will be of type gossh.ServerConn.
+	ContextKeyConn = &contextKey{"ssh-conn"}
+
+	// ContextKeyPublicKey is a context key for use with Contexts in this package.
+	// The associated value will be of type PublicKey.
+	ContextKeyPublicKey = &contextKey{"public-key"}
+)
+
+// Context is a package specific context interface. It exposes connection
+// metadata and allows new values to be easily written to it. It's used in
+// authentication handlers and callbacks, and its underlying context.Context is
+// exposed on Session in the session Handler. A connection-scoped lock is also
+// embedded in the context to make it easier to limit operations per-connection.
+type Context interface {
+	context.Context
+	sync.Locker
+
+	// User returns the username used when establishing the SSH connection.
+	User() string
+
+	// SessionID returns the session hash.
+	SessionID() string
+
+	// ClientVersion returns the version reported by the client.
+	ClientVersion() string
+
+	// ServerVersion returns the version reported by the server.
+	ServerVersion() string
+
+	// RemoteAddr returns the remote address for this connection.
+	RemoteAddr() net.Addr
+
+	// LocalAddr returns the local address for this connection.
+	LocalAddr() net.Addr
+
+	// Permissions returns the Permissions object used for this connection.
+	Permissions() *Permissions
+
+	// SetValue allows you to easily write new values into the underlying context.
+	SetValue(key, value interface{})
+}
+
+type sshContext struct {
+	context.Context
+	*sync.Mutex
+}
+
+func newContext(srv *Server) (*sshContext, context.CancelFunc) {
+	innerCtx, cancel := context.WithCancel(context.Background())
+	ctx := &sshContext{innerCtx, &sync.Mutex{}}
+	ctx.SetValue(ContextKeyServer, srv)
+	perms := &Permissions{&gossh.Permissions{}}
+	ctx.SetValue(ContextKeyPermissions, perms)
+	return ctx, cancel
+}
+
+// this is separate from newContext because we will get ConnMetadata
+// at different points so it needs to be applied separately
+func applyConnMetadata(ctx Context, conn gossh.ConnMetadata) {
+	if ctx.Value(ContextKeySessionID) != nil {
+		return
+	}
+	ctx.SetValue(ContextKeySessionID, hex.EncodeToString(conn.SessionID()))
+	ctx.SetValue(ContextKeyClientVersion, string(conn.ClientVersion()))
+	ctx.SetValue(ContextKeyServerVersion, string(conn.ServerVersion()))
+	ctx.SetValue(ContextKeyUser, conn.User())
+	ctx.SetValue(ContextKeyLocalAddr, conn.LocalAddr())
+	ctx.SetValue(ContextKeyRemoteAddr, conn.RemoteAddr())
+}
+
+func (ctx *sshContext) SetValue(key, value interface{}) {
+	ctx.Context = context.WithValue(ctx.Context, key, value)
+}
+
+func (ctx *sshContext) User() string {
+	return ctx.Value(ContextKeyUser).(string)
+}
+
+func (ctx *sshContext) SessionID() string {
+	return ctx.Value(ContextKeySessionID).(string)
+}
+
+func (ctx *sshContext) ClientVersion() string {
+	return ctx.Value(ContextKeyClientVersion).(string)
+}
+
+func (ctx *sshContext) ServerVersion() string {
+	return ctx.Value(ContextKeyServerVersion).(string)
+}
+
+func (ctx *sshContext) RemoteAddr() net.Addr {
+	return ctx.Value(ContextKeyRemoteAddr).(net.Addr)
+}
+
+func (ctx *sshContext) LocalAddr() net.Addr {
+	return ctx.Value(ContextKeyLocalAddr).(net.Addr)
+}
+
+func (ctx *sshContext) Permissions() *Permissions {
+	return ctx.Value(ContextKeyPermissions).(*Permissions)
+}